Open a TwinCAT 2 PLC project

Compilation

It must be possible to compile the project in TwinCAT 2.x PLC Control without compilation errors. Nevertheless, TwinCAT issues warnings during the compilation. These are caused by implicit conversions that can lead to the loss of information (for example due to the change of a sign).

TwinCAT 3.1 checks case statements against the switch variable: CASE USINT OF INT is not checked in TwinCAT 2.x, but there is an error message when importing into TwinCAT 3.1.

Libraries

All variables and constants used in a library also have to be declared in this library. It must be possible to compile the library in TwinCAT 2.x error-free.

Syntactic and semantic restrictions

• FUNCTIONBLOCK is no longer a valid keyword in place of FUNCTION_BLOCK
• A ":" must follow after TYPE (declaration of a structure).
• ARRAY initialization must be enclosed in parentheses.
• A local declaration of an enumeration is no longer possible, except within TYPE: in the case of a TwinCAT 2.x import a local enumeration declaration is automatically converted into an explicit type definition.
• INI is no more supported (you have to replace this in the code by the Init method).
• In function calls, it is no longer possible to mix explicit parameter assignments with implicit assignments. Therefore, the order of the parameter input assignments can be changed:
  fun(formal1 := actual1, actual2); // → Fehlermeldung
fun(formal2 := actual2, formal1 := actual1); // gleiche Semantik wie folgende Zeile:
fun(formal1 := actual1, formal2 := actual2);
• TwinCAT 2.x pragmas are not converted. They generate a warning in TwinCAT 3.1.
• The TRUNC operator now converts to the data type DINT instead of INT; in the case of a TwinCAT 2.x import, TwinCAT 3.1 automatically adds an appropriate type conversion.

Memory

• In contrast to TwinCAT 2, TwinCAT 3.1 has an 8-byte alignment. For further details and samples, see Reference Programming > Alignment.
• Instances of the data type STRING are pre-initialized in TwinCAT 2 by zeroing the entire memory area. In TwinCAT 3.1, however, only the first byte of such an instance is zeroed. Due to the null termination, the instance is also empty.

Placeholders and their replacement

Placeholder

VAR_INPUT

Use

Replacement

MAIN.$LocalVar$.aArr[0]

localVar: MyStruct;

localVar.aArr[0]

localVar := MAIN.myStructVar

$Var$.aArr[0]

Var : MyStruct;

Var.aArr[0]

Var := MAIN.myStructVar

MAIN.myStructVar.aArr[$Index$]

Index : INT;

MAIN.myStructVar.aArr[Index]

Index := 0

Problematic placeholders

• Placeholder within a text:
  Text: $axle$-Axis
  Correction:
  localVar : STRING;
  Text: %s-Axis
  TextVariable : localVar
• Placeholder describes only a part of a variable name:
  axis$axis$track$track$.fActPosition
  Correction:
  Define only one placeholder for the placeholder axis$axis$track$track$.
  axis_spur : MyFunctionBlock;
  Then pass the corresponding instance of the function block directly.
  axis_spur := MAIN.axis1spur2;
• Placeholder is replaced by an expression:
  $Expression$ → MAIN.var1 + MAIN.var2
  Correction:
  You must pass the expression to an auxiliary variable and then pass this auxiliary variable as an instance.
• Placeholder describes a program name: $Program$.bToggle → MAIN.bToggle D
  The converter cannot transfer this form of placeholder replacement to TwinCAT 3.1. However, they are rarely used in practice.
• Placeholder is replaced by different types:
  $Var$
  → Replacement 1 : MAIN.n (INT)
  → Replacement 2 : MAIN.st (STRING)
  Solution:
  Define two different placeholders in the interface.
• The visualization is located in a library. You only replace the placeholders later from any project when you use the visualization there.
  Correction:
  Here you must manually replace the TYPE_NONE data types. However, there is a possibility for you to integrate the library in a project and for the placeholder to be replaced properly. If you now import this project, the data type will also be determined correctly in the library.

Non-importable items

Trend, ActiveX – the import is not possible because the implementation is very different. In TwinCAT 3.1 a corresponding warning is given and a corresponding manual reconstruction is necessary.

Programming languages

ST, IL, FBD

No restrictions

LD

TwinCAT 3.1 imports function blocks with parallel branches so that the part before the branch is repeated for each branch. This corresponds to the generated code that TwinCAT 2.x generates for parallel branches.

SFC

• Step variables explicitly declared by the user must be declared locally in the SFC editor. You must not declare them as VAR_INPUT, VAR_OUTPUT or VAR_INOUT, because TwinCAT 3.1 cannot automatically adapt the calls. Explanation: Steps no more use boolean variables for the management of the internal states in TwinCAT 3.1, but also structures of the type SFCStepType.
• Identifier: The following identifiers may not begin with an underscore:
• Names of IEC actions in the tree
• Variables that are called in an IEC association list
• Names of programmed-out transitions

Explanation: Implicit variables that TwinCAT 3.1 creates for actions are given an underscore as a prefix in TwinCAT 3.1. An invalid identifier with a double underscore would result.

CFC

• Large function blocks: The layout of large function blocks may suffer a loss of quality as a result of the import; the function block box modules may overlap significantly.
• Macros: Macros cannot be imported.